<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <title>Document</title>
  <style>
    body {
      margin: 0;
    }
    #box {
      margin: 100px;
      width: 200px;
      height: 200px;
      background-color: red;
    }
  </style>
</head>
<body>
  <div id="box">
  </div> 
  <script>
    var box = document.getElementById('box');
    // box.onclick = function (e) {
    //   e = e || window.event;
    //   // 获取事件名称
    //   console.log(e.type);
    // }
    
    box.onclick = fn;
    box.onmouseover = fn;
    box.onmouseout = fn;

    function fn(e) {
      e = e || window.event;
      switch (e.type) {
        case 'click': 
          console.log('点击box');
          break;
        case 'mouseover': 
          console.log('鼠标经过box');
          break;
        case 'mouseout': 
          console.log('鼠标离开box');
          break;
      }
    }

  </script>
</body>
</html>
